The invention relates to a multiscale transient event detector for use in nonintrusive load monitoring.
Electric utilities and commercial facilities want to develop detailed electric power consumption profiles of their customers to aid in leveling peak loads and in planning future capacity. Conventional metering of individual appliances is costly and inconvenient to the consumer. These costs increase swiftly as data requirements become increasingly complex. The high cost of equipment continues to limit the amount of usage data utilities can collect. Additional drawbacks of the equipment now available for collection of end-use load survey data range from their cost, reliability, and flexibility to intrusion into the customer's activities and premises.
To deal with these concerns, utilities have sought a way of determining the operating history of an electrical load from measurements made solely at the utility service entry of a building. This problem is actually quite tractable under certain conditions. As a result nonintrusive load monitoring systems were developed. Nonintrusive load monitors (NILM) are intended to determine the operating schedule of the major electrical loads in a building from measurements made at the utility service entry. Conventional load monitoring schemes require separate metering equipment or connections for every load of interest. The feasibility of the nonintrusive monitoring approach for residential purposes has been demonstrated. However, fundamental limitations in the design of the residential NILM hinder its ability to operate in a commercial or industrial building, where appliances turn on and off frequently and substantial efforts, e.g., power factor correction, are made to homogenize the steady state behavior of different loads.
The advantages of nonintrusive load monitoring over conventional load monitoring include ease of installation at the monitoring site, since the nonintrusive load monitor (NILM) requires a single set of electrical ties. In addition, NILM offers simplification of data collection, since the NILM automatically determines the electrical nature of the simple, "two-state" appliances in a target building without the need for a load survey or inspection. Furthermore, NILM enhances facilitation of data analysis since, by definition, the NILM collects and potentially analyzes all data at a central location.
The NILM is more than a convenient and economical means of acquiring energy usage data. It is, for example, a potentially important platform for power quality monitoring. Utilities, manufacturers, and consumers are becoming increasingly aware of "power pollution" . Many loads, such as computers and other office equipment, lighting fixtures, and adjustable speed drive systems found in modern air handling equipment, may contain solid state switch mode power converters that could draw distorted, nonsinusoidal input current waveforms. These harmonic currents create harmonic voltages as they flow through impedances in the utility's transmission system, degrading the quality of the delivered voltage waveform. Power pollution has become more than an academic concern as consumers increasingly turn to power electronic solutions to increase efficiency.
Additional monitoring capability for harmonic current content would generally be cheaper and easier to install at a service entry location than on every load of interest. The NILM could track down power quality offenders by correlating the introduction of undesired harmonics with the operation of certain loads at a target site. Conventional implementations of the residential NILM track the operating schedules of the loads at a target site by looking for changes in steady state levels of real and reactive power. While informative in the residential setting, changes in steady state power levels are less revealing in commercial or industrial environments, where substantial efforts, e.g., power factor correction and load balancing, are made to homogenize the steady state behavior of different loads.
Fortunately, the transient behavior of many important load classes is sufficiently distinct to serve as a reliable indicator of load type. The present invention presents a transient event detector and process that can be used to identify observed transient waveforms even when multiple transients overlap. The detector and process are suitable for incorporation into an advanced NILM which would be capable of monitoring demanding commercial and industrial sites.